The Peripheral Component Interconnect Express (“PCI-Express”) standard defines how one or more peripheral devices can communicate with a computing device over a serial bus link. The serial bus link can be within a single computing device or can link one or more computing devices and peripheral devices. PCI-Express uses discrete logical layers to process inbound and outbound information. For instance, PCI-Express devices receive serial data, align the serial data and then convert the serial data into parallel data. PCI-Express devices use PCI-Express core logic for interfacing with host systems. The PCI-Express core logic includes a control status module (“PCS module”) that has a serial/de-serializer (“SERDES”) and other components. The SERDES in the PCS module communicates with a SERDES in a host system. However, before the SERDES in the PCS module can communicate with a SERDES in the host system, the PCS module detects if a receiver (i.e. the SERDES in the host system) is present and/or available to receive data.
In conventional systems, a SERDES vendor provides the mechanism to detect if a receiver is present. Often, the mechanism provided indicates that a receiver is present by using specific receiver detection protocol incorporating a set frequency, for example, 3 to 15 kilohertz if a receiver is present or above 30 kilohertz is a receiver is not present. Such proprietary conventional techniques have shortcomings. For example, detecting a receiver at a frequency of 3 kilohertz may cause delay and may take too long.
In addition, another prior art method and apparatus for detecting a receiver over a PCI-Express bus is to adjust a common mode voltage by current injection using a charge pump into one or more transmitter output nodes and detecting whether a receiver is present based on a voltage change rate. The current is injected by a charge pump under control of an amplitude control circuit. The charge pump consumes large amounts of power, and thus this prior art method is not appropriate for low power applications. Therefore, there is a need for a low power method and system to perform the receiver detection efficiently.